The overall objectives of this proposal are to identify biomarkers to diagnose and predict HIV immune reconstitution inflammatory syndrome (IRIS) associated with cryptococcal meningitis (CM) in AIDS patients at the Infectious Diseases Institute (IDI) in Kampala, Uganda and to better understand the pathogenesis of IRIS. IRIS is an exaggerated inflammatory response that occurs in a subset of patients with advanced AIDS after starting antiretroviral therapy (ART). In patients who develop IRIS, the improved immunity with ART leads to the development of exaggerated antigen-specific inflammatory responses directed against opportunistic infections (OIs), resulting in clinical deterioration. CM kills more people each year than any other AIDS-associated OI, killing approximately 700,000 people worldwide annually. IRIS associated with CM occurs in approximately 40% of patients with CM when they start ART. CM IRIS is particularly severe and approximately half of patients who develop CM IRIS die. IRIS results in unnecessary morbidity and mortality, threatens individual patient ART compliance and treatment success, and may potentially threaten societal acceptance of ART programs. The proposed studies will lead to a better understanding of CM IRIS immunopathogenesis and identify biomarkers of IRIS that can be used for prediction and objective diagnosis of IRIS. This program of research will be coordinated by the recently established Uganda-International Network for the Study of HIV IRIS (Uganda-INSHI) Collaborative Research Group which includes international research partners from Uganda, Europe, and the U.S. Specific Aim 1: To determine if biomarkers of immune activation expressed by circulating T-cells can be used to diagnose CM IRIS or predict those patients who are at risk for the development of IRIS. Specific Aim 2: To determine if persons who develop CM IRIS have an unbalanced immune reconstitution with a decreased Regulatory T-cell to Effector T-cell balance compared to persons who do not develop IRIS. To address these aims, we will collect blood from two groups of patients prior to and following initiation of ART: AIDS patients with CM (CM cohort) or AIDS patients with no known OI (No OI cohort). We will use flow cytometry of blood and CSF to analyze immune activation by the expression of cell surface biomarkers as well as biomarkers defining Treg, Th17, naive, and memory T-cell subsets. We will analyze the biomarker expression prior to ART initiation and after 2, 4, 8, and 12 weeks of ART as well as the time of any IRIS events and will compare the expression of these biomarkers in patients who do or do not develop IRIS in order to determine if specific biomarkers can be used to diagnose IRIS or predict those patients at risk for future development of IRIS. Understanding the expression of these biomarkers will provide insight into the pathogenesis of IRIS and will allow us to determine if these biomarkers would be useful clinically to diagnose IRIS or predict which patients are at risk.